1. Field of Invention
The present invention relates to methods for analyzing the effects of borehole, formation, fluid, and completion properties on the propagation of waves generated by water hammer. In another aspect, the present invention relates to methods and devices for mitigating the effect of water hammer in borehole completion equipment and in injectors. The invention can also be used to determine the properties and the changes in properties of completion and formation.
2. Description of the Related Art
Water hammer (or, more generally, fluid hammer) is a pressure surge or wave generated by the kinetic energy of a fluid in motion when it is forced to stop or change direction suddenly. For example, if a valve is closed suddenly at an end of a pipeline system a water hammer wave propagates in the pipe. In a production well or in a well being drilled, a water hammer may be produced if a blowout preventer (BOP) is activated in response to a detected influx of gas or fluid into a borehole. A water hammer may also be generated during a standard shut-in of a well. See, for example, SPE 00064297. The transient pressure associated with a water hammer may cause borehole failure and/or failure of sensitive electronic, electrical and electromechanical equipment in a well. For the purposes of the present invention, we refer to a “borehole system” as including the borehole and all devices attached to the borehole.
U.S. Pat. No. 5,220,504 to Holzhausen et al. discloses a method of determining formation properties such as permeability by setting up pressure oscillations in a borehole. The analysis is based on modeling of the earth as a homogenous medium (with possible fractures therein) surrounding a fluid filled borehole. The methodology is of little use in a real production borehole which may include production tubing, casings of different sizes, cement, perforations, packers and sand-packing. The present invention is directed towards analysis of real production boreholes that may have both radial and vertical variations.